I think Paddy has hit the nail on the head.....cheap conversions that add a lot of power to an engine,and that includes crummy turbo or supercharger conversions as well as poorly implemented nitrous kits,are an excellent way of finding out which parts of the drivetrain and engine aren't quite up to the job.
It's all very well adding shall we say 100bhp to the car,but if the pistons,rods,crank,clutch and so on are not built for it then the result is obvious.